Objective To investigate the prevalence of diabetes mellitus and the characteristics of their comorbidities among the elderly hospitalized patients in order to supply epidemiological and clinical data. Methods The clinical data about the information on the first page of medical records of 22 374 elderly inpatients in Beijing Friendship Hospital during the past 5 years were reviewed and statistically analyzed. Results The prevalence of diabetes mellitus was 22.07% for the patients with the age younger than 60 years, while, with the growing of age, the prevalence was increased by 0.89% every 5 years. Thus, the total prevalence of diabetes mellitus of the cohort was increased up to 29%. The most common comorbidities of the cohort were hypertension, cardiovascular disease, cerebrovascular disease and hyperlipemia. Conclusion The prevalence of diabetes mellitus is obviously higher in the elderly than in non-elderly patients. Clinicians should pay more attention to the screening and prevention of common comorbidities in the elderly diabetic population.